Never seen a plastic or porcelain lamp holder with a receptacle that was anything other than two prong.
Personally, I prefer the old porcelain lamp holders, just be careful with the screws to not chip or break the fixture. Put two or three in the attic with a switch at the entrance. install CFL bulbs and when you forget to turn them off, you won't waste much electricity or generate much heat.
Charles
Usually the porcelain pull chains have the 3 prong outlets now,don't recall if the plastic ones have it.